For the purpose of automating cooking appliances, such as an electronic range, an electric oven, etc., there have already been developed a method in which the water vapor and various gases released from a food are detected by a sensor means and the heating temperature is accordingly controlled. The sensor means usually employed in this type of cooking appliance includes a heating element as disposed near the sensor element so as to vary the sensitivity of the sensor element or protect the sensor element against accumulation of dust from the ambient atmosphere and from vaporized oil, etc. from the food. A sensor means developed earlier includes a coil-shaped heater element 26 (see FIG. 3) around a sensor element 1 and the two elements are electrically separated from each other. Thus, as will be apparent from FIG. 3, the electric signal supplied to the coil for causing the coil heater 26 to generate heat does not exert any influence on the impedance detection signal of the sensor element 1 and, therefore, the impedance of sensor element 1 can be easily detected. However, despite the above-noted advantage, the sensor means of this type is disadvantageous in that because the coil heater 26 and sensor element 1 are disposed in a spaced-apart relationship, the heater 26 must be supplied with a relatively large electric power in order to heat the sensor element 1 and in addition, the heater 26 and sensor element 1 must be securely held in position in order to maintain their delicate spatial relationship.
To obviate the above-noted disadvantage, it might be contemplated to construct a sensor means having a high thermal efficiency by integrating a heating element and a sensor element as a single unit. However, it is quite likely that, in such an integrated setup, the electric signal applied to the heating element influences the impedance detection signal of the sensor element.
This invention provides a sensor control arranged such that the electric signal applied to the heating element does not influence the impedance detection signal of the sensor element.